A lithium secondary battery includes a solid electrolyte, and positive and negative electrodes that are arranged so as to sandwich the solid electrolyte. Accompanying the recent trend toward thinner lithium secondary batteries, it has become necessary to reduce the thickness of a solid electrolyte. As a method for reducing a solid electrolyte thickness, a deposition technique can be considered.
However, because of the complex composition of the solid electrolyte used for the lithium secondary batteries, a solid electrolyte with excellent characteristics cannot be formed easily by the deposition technique. Further, there has been a problem that the deposition technique cannot be carried out with sufficient productivity.